A bandgap voltage reference is a voltage reference that is widely used in integrated circuits. The bandgap voltage reference circuit generally uses junction-isolated bipolar-IC technology to make the stable low-voltage reference. The bandgap voltage reference has become popular as a stable voltage reference for low-voltage circuits. For example, bandgaps have been used in digital integrated circuits to provide a local bias that is not adversely affected by ambient noises or transients.
Contactless card applications, which involve communication between a reader and a contactless card via a carrier signal, have also used the bandgap as a reference voltage. Specifically, in these applications, powering on and off the contactless card's circuit can be critical since the power supply may perform sequences of false starts, i.e., sudden drops and quick restarts. In the absence of an appropriate startup or restart procedure, these circuits can be driven into incorrect operation.
In particular, analog functions of a contactless card can rely on a bandgap voltage reference, and in some situations, these analog functions must be disabled if the bandgap circuit is not operating correctly. Furthermore, merely delaying the circuit's operation does not guarantee correct operation because, for example, during a fast power off/on sequence, the circuit will restart with the delay being disabled since the circuit did not fully discharge. As a result, the circuit of the contactless card may begin operating incorrectly.